In a system such as a machine tool that is driven using a synchronous motor, if the commanded acceleration is large, the maximum torque of the synchronous motor may be exceeded and the motor may become unable to be operated as commanded. Similarly, depending on the inductance of the synchronous motor, if the commanded jerk is large, the commanded voltage of the synchronous motor may exceed the maximum voltage of a current amplifier and the motor may become unable to be operated as commanded. The condition in which the commanded voltage of the synchronous motor exceeds the maximum voltage of the current amplifier is called the “voltage saturation”.
In view of the above, there is proposed a control apparatus that detects whether or not the commanded voltage causes voltage saturation (for example, refer to Japanese Unexamined Patent Publications No. JP-A-2000-341991, or JP-A-2003-209996). FIG. 1 shows the configuration of a motor control apparatus according to the prior art. The prior art control apparatus comprises: a saturation detector 1009 which detects whether the magnitude of the voltage command applied to a power converter 101 exceeds the maximum voltage that the power converter 101 can apply to a PM motor 1002, and which outputs a voltage saturation signal that is set to “−1” when the maximum voltage is exceeded and voltage saturation has occurred, and otherwise set to “1”; and a magnetic flux current adjuster 1010 which, when the voltage saturation signal output from the saturation detector 1009 is “1”, causes the d-axis current idc to gradually increase in the positive direction until reaching a predetermined upper limit value and, when the voltage saturation signal is “−1”, causes the d-axis current idc to gradually increase in the negative direction until reaching a predetermined lower limit value. With the above configuration, it is possible to automatically adjust the magnitude of the d-axis current idc and thereby prevent the voltage command Vc from exceeding the maximum voltage Vm that the power converter 101 can output. Further, the q-axis current and d-axis current can be made to follow their current commands. Thus, even when the voltage is saturated, operation can be continued and, when the voltage is not saturated, the operating state with maximum efficiency can be achieved.
As described above, JP-A-2000-341991 (hereinafter, referred to as “patent document 1”) discloses detecting and outputting voltage saturation and reducing the current command value. However, while patent document 1 describes that the current command value is reduced in the case of voltage saturation, reducing the current command value results in an inability to produce torque as commanded by a torque command. As a result, the tool cannot be moved to the commanded position at the commanded speed in order to generate the commanded shape; in particular, when generating the contour shape of a workpiece by controlling a plurality of axes, there arises the problem that the accuracy of the shape degrades.
It is an object of the present invention to provide a motor control system that has the function of suppressing the commanded jerk by detecting the presence or absence of voltage saturation and by notifying a host control apparatus of the result of the detection.